The purpose of this study was to evaluate the effect of postmenopausal estrogen replacement on apolipoprotein B metabolism (VLDL & LDL using endogenous, stable isotope labelling, conclusions: 1) oral estradiol, 2mg daily, reduces LDL concentrations by 12%, primarily by increasing LDL catabolism by 38%. This accelerated catabolism overcomes the tendency of estrogen to increase LDL production by 21%. 2) TD E suppressed FSH to a greater extent that did PO E (44% vs. 33%).